FILTRATION AND BACKWASHING. A. Amirtharajah School of Civil and Environmental Engineering Georgia Institute of Technology Atlanta, GA 30332. FILTRATION: THE GREAT BARRIER TO PARTICLES, PARASITES, AND ORGANICS. Particle Removal. Improve taste, appearance Sorbed metals and pesticides
School of Civil and Environmental Engineering
Georgia Institute of Technology
Atlanta, GA 30332
Phenomenological - Macroscopic View
0.01 -0.025 mm
3 - 5mm
6 - 10mm
dp < 1 mm
dp > 1 mm
Trajectory Analysis - Microscopic View
Ginn et al.:
Filter coefficient ()
Why is it easier to remove alum or clay particles in contrast to polymer coated particles or micro-organisms during backwash?
Van der Waals Force:
Electrostatic Double Layer Force:
Hydrodynamic Forces > Adhesive Forces
1. Spherical Particles - pH and Ionic Strength
2. Non-spherical Particles - Ionic Strength
The best for cleaning
a, b = coefficients for a given media
Qa = air flow rate
Percentage of minimum fluidization
Potential Energy of Interaction
polymeric substances at
Nieminski and Ongerth (1995)
In the multiple-barrier concept, filtration is the “great” barrier to particles, parasites and organics.
This paper includes the work of several former students at Georgia Tech:
M.S. students T.M. Ginn, L. Zeng and X. Wang and Ph.D students, Drs. P. Raveendran, R. Ahmad, K.E. Dennett and T. Mahmood.
They were not only students but teachers too! Their work is acknowledged with gratitude.